The invention relates to a method for ultrasound imaging of tissues located in a tissue image region, that includes the steps of:
a) Projecting at least an ultrasound beam into the tissues image region;
b) Receiving ultrasound reflections of the at least one projected ultrasound beam from the tissue image region and transducing the reflection into corresponding electrical echo signals;
c) Processing the echo signals according to at least two different modes;
d) One of the processing modes being an imaging mode furnishing a panoramic image of the region under examination;
e) The other at least further processing mode being a different processing mode for imaging particular tissues or tissue structures or physiological flows.
Different modes of evaluating the ultrasound beams reflections for reconstructing useful diagnostic images of internal tissues are known and used in the ecographic imaging devices.
Each different mode has been developed for achieving useful diagnostic images of the internal tissues. Particularly recent imaging modes lead to images which evidence the pathology searched but only for the specific tissue without combining this visual information with a general view or panoramic view of the region where the particular tissue is located or embedded. This gives rise to difficulties in driving the apparatus in a correct way, since the user normally brings the ultrasound probe manually in position at the body to be examined. In absence of a general view of the region under examination the user has no way to orientates itself in order to find the correct position of the probe for taking an image of the tissue to be imaged.
This situation gets worse if one considers that most of the alternative imaging modes such as Doppler or power Doppler modes and all the so called Harmonic Imaging modes leads to a signal only with a certain delay and in some cases also only when the specific tissue is correctly pointed by the scanning beams emitted by the probe.
Furthermore, the actual imaging modes are all separately exploited. So many advantages residing in the mutual integration of the information which may be extracted by the different modes from the reflected signals are lost.
From the point of view of the treatment of digital images a combination of the information of two or more images of the same object may be a simple way to solve the problem. However in the case of diagnostic images the problem lays in the fact that not each kind of combination may lead to the construction of an image having improved information content for diagnostic examinations.
A further problem which renders the use of combined imaging techniques less interesting consists in the fact that in order to allow simple and effective examinations and to obviate to the actual difficulties of the user in correctly handling and moving the probe, a real time output of the images is aimed. This requires very high acquisition and/or computing rates and thus expensive hardware configurations. In order to limit the expense normally a compromise is chosen which depending on the imaging mode may lead to a so called quasi real time output of the images, i.e. to image information extraction and image reconstruction times which are relatively short in order to resemble roughly to a real time function.
As it might be understood from the above there are two technical problems which solutions contrast one against the other in the sense that a solution of one of the said problems means a worsening of the conditions for solving the other problem.
The present invention aims to solve the aforementioned problems by providing a method for ultrasound imaging of tissues which allows to produce better or more complete images of tissues from the point of view of the intelligible information brought to evidence therewith and having better visual appearance.
A further object of the present invention is to provide for particular embodiments of the aforementioned method which may be useful for extracting special information from the images acquired.
The inventions solves the above mentioned problems with a method for ultrasound imaging as described above which comprises in combination the following steps:
h) Displaying the images obtained by processing with the at least two modes in an interleaved or combined, particularly superimposed manner on the same screen;
i) The B-mode image being displayed with a black and white or gray- scale image;
j) The image of the at least one further processing mode being displayed in a colored manner by choosing a color adapted to the optimum physiological capability of human eyes to discriminate the information displayed by the color level scale.
In a preferred embodiment method the color chosen is within the green to yellow wavelengths interval.
Using this kind of combination the information according to the different imaging modes gives the possibility of viewing at the same time or in a same image a particular object which may be successfully or better revealed by a special or particular imaging mode and region in which this object is embedded.
In moving the probe during scanning the user may have the possibility to know at every moment where he is directing the probe within the body under examination and may rapidly correct the probe position and/or orientation if this two parameters have not been correctly chosen. This reduces the examination duration particularly when the examination requires invasive techniques such as Harmonic Imaging with injection in the region to be imaged of a contrast medium. Indeed this medium will rest in the region to be imaged and in the particular object to be examined only for a predetermined and limited period of time.
The said B-mode image may be reconstructed from reflected beams at the fundamental frequency of the projected beams or at a subharmonic or harmonic frequency of the projected beams (Harmonic B-mode Imaging).
The second processing mode may be any kind of signal processing actual or future and for example it may be a mode using physical effects on the reflected echo signals such as frequency shifts or changes in the frequency spectra of the reflected echo signals as for example the so called Pulse Inversion imaging mode.
According to the so called Pulse Inversion mode two successive beams are projected into the region under examination for each scanning line the second beam being inverted with respect to the first beam. The two reflected beams due to the two projected beams are then summed together. Other kind of combination of differentiation of the reflected beams due to two or more successive projected beams along the same scan line may be used and are known in the art.
An alternative second processing mode is a so called Harmonic Imaging mode, being the echo signals received at a different frequency of the fundamental frequency of the projected ultrasound beam and/or being extracted from the echo signals the part of said echo signals within a certain frequency spectrum or having a certain frequency different from the fundamental frequency of the ultrasound beam projected. Particularly reflected echo signals having an harmonic or subharmonic frequency, commonly a frequency corresponding to the second harmonic of the fundamental frequency of the projected ultrasound beam are used.
Alternatively also the so called Doppler o Power Doppler modes may be used as the second processing or imaging mode.
As it might appear from the above, the mentioned processing or imaging modes are not limited to the use as a second imaging mode, the images reconstructed therewith are used to be combined with the images resulting from the first processing or Imaging mode. Indeed it is possible to use also as a first processing or imaging mode one of the above imaging modes indicated for the second processing or imaging mode.
It is also clear that a further development of the present invention may consist in processing or reconstructing images from the received reflected beams according to three or more different processing or imaging modes of the kinds listed above.
In this case many combinations of modes may be achieved and many way of displaying and combining the corresponding images are possible.
According to a first example of combination of the images obtained by the three different imaging modes, there are displayed alternatively or side by side at least two or three images relating to the combination of the information of the first and second processing mode and of the first and third processing mode and or of the second and third processing mode.
In this case there might be an automatic time sharing program of the display monitor for each image or a manual selection by the user.
A further option may consist in the fact at least two of the three combination images are displayed adjacent to one another in different areas of the display screen, while the third combination image is displayed alternatively to one of the first two images either by automatic time sharing of the display or by manual command.
Alternatively the three combination images are displayed at the same time in partial areas of the display screen.
Another feature consists in the fact that the first processing or imaging mode is a so called B-mode, the second processing or imaging mode is a so called Harmonic Imaging mode or Pulse Inversion mode, the third processing mode is a so called Doppler or Color Doppler or Power Doppler mode.
In this case at least two. of the three combination images are displayed relating to the combination of the information of the B-mode and of the Harmonic Imaging or Pulse inversion mode and according the combination of information of the B-mode and the Doppler or Color Doppler or Power Doppler mode. A third image is obtained from the combination of information of the Harmonic Imaging Mode or the Pulse Inversion Mode and of the information of the Doppler, or Colour Doppler or Power Doppler mode and may be displayed either with the preceding two combination images or with one of the preceding two images, or alone.
Other combinations may be used as well as the combinations of a first mode, as the B-mode with one of two further different modes which are different also one with respect to the other.
Also the kind of combination of two modes may be executed in different ways.
One first way of combining the information or the images of the at least two imaging modes according to the present invention consists in the fact that the two images are simply superimposed.
According to a further improvement the image displayed is a weighted combination of the image processed with a first processing mode and of the image processed with at least a second processing mode.
As an example of a weighted combination the following algorithm may be used:
alpha*first-mode+(1-alfa)*second-mode
with alpha being variable between 0 and 1.
A further way of combining the information or images according at least two imaging modes consists in modulating some parameters of the image of a first processing mode by means of the information obtained by the at least one second processing mode.
Color images on the display are formed by an ensemble or an array of luminous dots. In a black and white matrix of such dots, called pixels, the value corresponds to the intensity of the pixel which variation defines a gray-scale from white to black. Using the signals to drive the display obtained by the B-mode Imaging process leads to an image in gray-scale. The signal corresponding to a scanning line, and thus to a reflected beam has a structure variable in time and time is correlated to the depths of penetration of the signal in the examined body. Thus by means of the velocity of propagation of sound in the body it is possible to univocally correlate the level of the reflected signal related to this line at a certain moment to a certain depth. Thus by digitalizing the signal corresponding to a reflected beam it is possible to construct a vector in which signal intensity is correlated to the depth. This vector is then transformed in driving signals of pixels of a pixel matrix aligned on a line and each pixel or group of pixels along this line will be driven at an intensity or luminosity, i.e. at a white, gray or black level corresponding to the signal level of the vector components. In this case it may be said that the image data obtained by the B-mode drives the value of the pixels.
It is to be stressed that the example with the line is made in order to facilitate comprehension but it is easy to understand that this concept may be applied also considering a two-dimensional matrix corresponding to several adjacent lines or to a three-dimensional matrix.
Such a gray-scale or black and white image may then be colored. In order to color a black and white or gray scale image two parameters are available. First of all it is possible to give a range in which the color may vary. It is possible to chose only one color such as a yellow, green or blue -scale or a range extending over wavelength corresponding to more colors. Technically this parameter is called the Hue and it defines the kind of color. Driving this parameter does not mean that the image is colored but that if it will be colored the range will be that defined by the chosen Hue parameter. The second parameter makes sure that the image is colored according to the hue defined. This parameter is called saturation and it gives the level of presence of color. If the saturation is zero we still have a gray-scale or black and white image. By increasing the saturation to the gray scale the colors are mixed according to the hue that has been chosen. Very low values of saturation will color the gray-scale image weakly as if a colored transparency has been superimposed on the black and white or gray-scale image. Higher levels of saturation will cover more and more the gray-scale or black and white image which becomes a fully colored image. Thus this coloring method may be used in such a way as to combine the information of the two imaging modes in order to display an image that intuitively depicts the situation relating to the information acquired by the second imaging or processing mode from the region under examination or from only a part of it.
According to the present invention a way of combining the information or images of the two imaging modes consists in displaying the image by means of a Hue-Saturation-Value transform (HSV) by defining a constant value for Hue at a wavelength at which human eye""s sensitivity is higher, particularly in the green to yellow wavelength range, and by modulating the Value by means of the information obtained with a first processing mode (particularly a B-mode) and by modulating the saturation by means of the information obtained with a second processing mode (as for example Harmonic Imaging mode).
This means that the first imaging mode gives a pure black and white or gray-scale image of the scanned region while the information of second imaging mode is displayed by the color defined through the constant hue range and the appearance of the color on the black and white or gray-scale image is more or less present depending on the level of the image data according to the second imaging mode.
Considering for example a B-mode image of an interesting region, this method will display a gray-scale image of the region. Typically for example in human tissues the B-mode image depicts very good the substantially stationary tissues and corresponds to a general view of the region under. examination which is scanned.
When a second Imaging mode is used for imaging for example contrast media perfusion/vascular flow, such as Harmonic imaging, Pulse inversion or Two or more Pulse combination modes the data obtained by these modes will determine the more or less color presence defined by the hue range chosen. This color will appear only in the zones of the image where a blood flow/contrast perfusion exists and the color saturation may indicate the intensity or density or the blood flow/contrast perfusion. Thus the combined image obtained does not.give only intuitive information about the existence of a bloodflow/contrast perfusion and the location of the flow/perfusion in a region under examination, but also gives intuitively understandable information about the intensity and/or density and or velocity of the flow/perfusion. This information may be read directly from the graphical appearance of the image displayed.
Instead of a HSV palette a HIS or a HLS palette may be used for forming an image displaying at the same time the information obtained from a first and from a second imaging or processing mode.
When three imaging or processing modes are considered instead of only two, such as for example a B-mode Imaging, Harmonic Imaging and Doppler or Power Doppler imaging, the third imaging or processing mode may be used for driving the Hue range thus adding more information. In this case Doppler or Power Doppler imaging for example of vascular or other physiological flows are measures of the velocity or intensity of movement and a different color may be associated with different velocities or movements intensities of the flow, while the saturation driven by the Harmonic Imaging mode gives a measure of the amount of contrast. media in each resolution cell
Another way to combine the information of two images modes consists in applying a palette representation based on a Hue-Saturation-Value (HSV) transform, which uses Hue=constant (corresponding to a wavelength at which human eye""s sensibility is higher, that is, chosen in the green/yellow wavelengths"" interval), Saturation=Contrast channel and Value=alfa*B-Mode+(1-alfa)*Contrast
Defined as the above the Value channel can be considered as an information from B-Mode modulated by the Contrast on the basis of the weight parameter xe2x80x9calfaxe2x80x9d. The effect to adopt such a representation is to have a color image of the Contrast with in transparency visualized B-Mode. The effect of a transparency is controlled by xe2x80x9calfaxe2x80x9d, that is alfa=0 means no transparency, alfa=1 means full transparency.
Choosing a proper value for xe2x80x9calfaxe2x80x9d would allow to have the desired underlying B-Mode information
In a more general embodiment we can imagine to mix three different information sources (e.g. B-Mode, Harmonic B-Mode, Doppler) by driving with their proper linear/non linear combinations the three channels of an HIS, HSV, HLS palette.
All the above mentioned steps of the method according to the invention do not consider the way with which the reflected beams are generated and the way to process them.
According to a first embodiment or option of the method of the present invention, the different imaging modes are used for evaluating the signals of the same reflected beam being originated by the same projected beam focussed along one scan-line in a predetermined scan-plane or slice of the region under examination.
In this case the digitalized signals may be processed in parallel by two or more signal processing channels which are optimized for a specific imaging mode of the two or more imaging or processing modes provided. Such a parallel processing option of the received signals for each imaging or processing mode has the advantage to be very fast but requires physically two signal processing channels and determines increased hardware costs.
Alternatively or in combination with the above option in the particular case of more than two imaging modes, only one signal processing channel may be provided which is driven by multiplexing in order to process the received signals according to the different imaging modes. In this case the need for hardware is reduced, however, in order to optimize the processing channel for processing the signals according to each of the imaging modes, a more flexible hardware is needed which may also be capable of saving in a memory different parameters setting for the different imaging modes. These parameter settings must be loaded in the hardware each time the multiplexing protocol addresses a different imaging mode.
When more than two imaging modes are provided it is important to understand that there might be only two processing channels which may be driven in parallel for processing two of the three processing modes and by multiplexing the input of the two channels between the two processing modes and the third one.
The above mentioned options may be also applied in combination with a. further improvement of the method which comprises that for each imaging method an optimized projecting beam is generated which causes a corresponding reflected beam optimized for one of the imaging modes provided. The two or more projected beams, depending on the number of chosen different processing modes which needs an optimized projected beam are fired one after the other with a short time delay along the same scan-line.
For example, desiring to collect a B-mode and an Harmonic Imaging mode image, along the same scan line two ultrasound beams are projected one after the other in the region under examination each one being optimized for one of the two modes and each one of which causes a reflected beam respectively optimized for B-mode Imaging and for Harmonic Imaging. The received signals may then be processed in parallel or by multiplexing according to the above mentioned options.
It has to be considered that some Imaging modes such as Pulse Inversion, or Pulse Differentiation modes need for themselves that two or more ultrasound beams are projected along the same scan-line. In this case, depending on the further imaging modes to be combined, one of the reflected beams due to one of the said projected beams may be used or a new ultra-sound beam may be projected into the region under examination along the same scan-line.
As far the described method may lead to long acquisition times for each image. In order to shorten the imaging time, the present invention suggests to process or to generate different projecting beams for different reflected beams along each scan-line (depending on which of the above options has been chosen) for one of the two, three or more imaging or processing modes whose image data has to be displayed in a combined manner only for part of the scan-lines which form an image scanning plane or slice through the region under examination.
Considering that each image. along a predefined image scan-plane is formed by a certain number of adjacent scan-lines, it is possible. to choose any combination of number of lines and positions of the lines in the slice or scan-plane to be processed according to the two or more imaging or processing modes or only to one or less than the maximum number of processing modes provided.
For each imaging or processing mode of the at least two or more imaging or processing modes the signals of the reflected beam along a different number of scanlines is chosen among the total number of scan-lines forming a slice or scan-plane through the region under examination, the received signals due to the reflected echoes along the said chosen scan-lines is processed according to the corresponding imaging mode.
This means that assuming that a slice or scan-plane through a region to be examined is formed by a certain maximum number of scan-lines, the received signals due to the reflected beams along all or only along certain specific or selected scan-lines is processed according one of the two or more of the imaging modes provided, while the signals due to the reflected beams along selected scan-lines is processed only accordingly the other of the two or more of the imaging or processing modes provided or according to only some or all of the said processing or imaging modes provided.
Assuming for example the choice of processing the ultrasound echoes according to the B-mode and to Harmonic Imaging mode, it is possible to process the ultrasound echoes along all scan-lines forming the scan-plane or slice according to the B-mode, while only a limited number of the total number of scan-lines is processed according the Harmonic Imaging mode or by both the said modes. The above teaching may be extended also to situations where three or more processing or imaging modes are chosen, and every kind of combination or selection of scan-line may be used, also by choosing different scan-lines or partially coinciding scan-lines for each mode. The choice of the scan-lines to be processed with one of the two or more imaging modes is not limited to the number of scan-lines but also to their location in the array of adjacent scan-lines forming the scan-plane or slice.
Thus for example adjacent scan-lines may be processed only with one of the two or more processing or imaging modes.
In a different embodiment, groups of adjacent scan-lines covering one or more partial regions of the entire scan-plane or slice may be processed according to one or more different processing or imaging modes while all the scan-lines are processed according one or more other imaging or processing modes.
This feature of the method according to the present invention allows to limit the processing times, since the double triple or multiple processing according to the two, three or more of the processing or imaging modes provided can be limited only to certain regions in which the use of alternative processing modes is useful or necessary for obtaining images of the particulars searched.
It is to be stressed out the every combination of choice may be made according to.the above mentioned feature.
It is also to be stressed out that the possibility of choosing the kind and the number of processing modes that will be used to process the received signals along each scan-line allows to influence two parameters, namely: the region of the scan-plane or slice the signals received from which may be processed by one or more further processing modes, as explained above, and also the density of the scanning lines the receiving signals along which are processed according one or more further processing or imaging modes.
In a particular case where only two imaging modes are used, for a first echo signal processing mode as the so called B-mode the maximum possible scan-lines are chosen, while for the at least second echo signal processing mode a reduced number of scan-lines is chosen either by limiting the density of the scan-lines or by limiting the width of the scan-region with respect to the maximum possible width of the said scan-region or by choosing more than one limited regions distributed over the scan-plane or slice.
Using for example the ultrasound imaging technique for acquiring internal images of a human or animal body, and desiring to image a predetermined limited region of this body and the vascular flow activity. in this predetermined region under examination it is possible to process the received echo signals of all the scan-lines forming the scan-plane or slice according to the B-mode, and to limit the processing according to the processing or imaging mode optimized for detecting vascular flow only for the scan-lines which forms the part of the scan-plane coinciding with a limited zone of the said region under examination where the blood vessel are located. In this case a first B-mode image covering the entire region may be acquired and then the parameters limiting the part of the scan-plane or slice coinciding with the zone where the blood vessel are located or with the region where the vascular activity is of interest may be defined with the help of the B-mode image. The scan-lines corresponding to the said zone may then be identified and the signals of the reflected beams along this selected scan-lines may be processed according to the second imaging or processing mode.
A further improvement may consist in the fact that at the border regions of the part of the scan-plane or slice, the corresponding scan-lines are processed according to the at least further processing or imaging mode, some more scan-lines located outside of this part of the scan-plane or slice may be also processed according to the said further processing or imaging mode, the density of this lines being reduced with respect to the normal one. This means that in the border regions outside of the said part of the scan-plane the signals relating to reflected beams along only a reduced number of scan-lines are processed according to the at least further processing or imaging modes, the said scan-lines being chosen not adjacent one to the other but separated by other scan-lines which are processed only according to the first processing or imaging mode.
Thus the image obtained according to the said at least further processing mode will have a lower definition at the border regions allowing to enlarge the field of view without reducing too much the overall imaging time.
This feature of the method according to the present invention is particularly useful considering the use as one of the processing modes of the Harmonic Imaging modes combined with contrast media. Contrast media are injected in the region under examination and provides enhancing effects for imaging vascular or similar physiological flows and/or stationary contrast media bubbles in the region under examination. Contrast media have a limited lasting time within the region of interest and their concentration due to the transport of the contrast media microbubbles by the flow slowly increases after injection and then again decreases. Thus long lasting imaging methods have the drawback that the image may be acquired when the contrast media concentration is too low in the region under examination. In this case there will be no sufficient time for repeating the image acquisition again and there might be the necessity of undesirable repeated contrast media injections in the region under examination. Too long lasting imaging methods further may fail with contrast media because the user may orient wrongly the probe imaging a completely wrong region or only partially the region of interest with the need also in this case of undesirable repeated injections of contrast media.
Reducing the time for acquiring an image will drastically reduce the need of repeated injection of contrast media in case of failure of the synchronisation of the acquisition of the image with the perfusion of contrast media in the region under examination or of a wrong orientation of the probe. After having displayed the first image there is sufficient time left for further correct image acquisitions. In case that no such failures occur more time is left for acquiring images of the interesting regions and an higher frame rate may be achieved.
It is important to understand that although the above mentioned method is described only with respect to the provision of the processing of the received signals corresponding to the reflected beams according two or more processing or imaging modes, the principle mentioned above may be also applied to the projection of multiple beams along the same scan-line. In this case according to the present invention the choice is provided to select for each single scan-line if along this line there must be projected only one beam or more subsequent beams each optimised for one or a part of the processing or imaging modes.
According to an further improvement of the method of the present invention which may be provided alone or in combination with the other steps or features, a shortening of the image acquisition may be achieved by means of the fact that the received echo signals of at least one or more or of at least part or of all the scan-lines are processed at least partly according to only one of the two processing modes and partly according to the other processing mode or according to a combination of the two processing modes by processing the time dependent signal of the reflected beam along the said scan-line with only one of the said two processing mode or with both modes for different parts corresponding to different or at least overlapping time periods of the duration of the reflected signal, which time periods corresponds to information reflected by tissues at different depth in the direction of the scan-line along which the projected beam has been focussed.
The reduction of the information that is to be processed by means of two or more processing modes deriving form the limitation of the part of the signal according to time automatically reduces the overall duration of imaging. The line limitation may be chosen in such a way that the reflected signals from a certain depth range in the region under examination are chosen. This may be achieved in a similar way as to the choice of the limited number of scan-lines which signals have to be processed according to the further processing mode, by acquiring and displaying a complete B-mode image of the region and than by defining the time interval of the received signals to be processed with the further processing or imaging modes by means of the B-mode image of the entire region.
Obviously instead of a B-mode image, the entire image of the region under examination may be constructed by means of other processing or imaging modes.
Combining this feature of the method according to the invention, i.e. the limitation of differential and/or parallel multiprocessing of the signals by defining time limited parts of the signals, with the limitation of differential and/or parallel multiprocessing of the signals by means of limitation of the number and/or location of the scan-lines will lead to a further reduction of the total imaging times.
It is further to be stressed out that the two above mentioned teachings for limiting the overall duration of imaging may be provided either alone or in a combination with the method steps for displaying in a combined manner the image data obtained by two or more different imaging modes.
Another feature of the present invention which can be provided separately or in combination with one or more of the above mentioned features regards method steps for measuring the perfusion of a contrast medium in a region under examination.
The measurement of perfusion curves by mean of ultrasound imaging may be obtained by injecting a contrast medium in the region under examination and by emitting particular projected beams for exciting a beam reflection which is sensitive to the vascular flows as for example according to the Harmonic Imaging mode or other kind of imaging modes. The projected beam may have a reduced or limited mechanical index at a level lower than the mechanical index needed to destroy or burst the contrast media micro bubbles. Alternatively the mechanical index of the projected beams may be sufficiently high to destroy a certain part of the microbubbles.
The evolution of contrast media enhancement or perfusion as a function of time in the region under examination is then detected by firing successive ultrasound projected beams covering the region under examination of the tissue imaging region. The time between injection of contrast media and instant at which firing of the ultrasound projection beam occurred or the time passed between the firing of each subsequent projection of a beam along the same line is then measured. The time measured being univocally correlated to each projection beam and to the corresponding reflected echo signal and the image data are stored in a image memory according to a image sequence based on the measured time at which each image has been acquired. Each time correlated image obtained and stored is then displayed in a film like succession.
For instance, in the case of liver scanning, the above mentioned method steps allow to make comparison between venous or arterial perfusion curves in a region under examination and a sample or samples of typical venous or arterial perfusion curves of other tissues which may show a particular pathology or which does not suffer of any pathology. The difference may be enhanced on the display by displaying in combined manner and with a predetermined color the differences or the two perfusion behaviors according one or more of the previous method steps for combined display of image data having different origin or obtained by different processing or imaging modes.
Similarly also a comparison between arterial and venous perfusion of contrast agents in the same tissue or region under examination may be made. This may help in enhancing features for better signal the presence of certain pathologies. In this case, in a tissue imaging region comprising arterial and venous blood vessels an image is displayed obtained by combining information processed according to B-Mode imaging of the tissue and information processed according to the second processing mode of the. arterial blood flow. This image is compared to an image representing a combination of information obtained by B-Mode imaging of the tissue and information obtained by the second processing mode of the venous blood flow. A time correlated image sequence may be acquired for both arterial and venous flows and the two image sequences may be compared one with the other and/or with typical sequences related to arterial and/or venous flow obtained by acquisition of images of a tissue showing a particular pathology or not showing any pathology at all.
A further possibility of comparison may take into consideration the comparison of contrast media perfusion behavior in the arteries and/or in the veins in a region under examination with the behavior of contrast media perfusion in particular samples tissue kinds.
According to yet another variant of the present method, successive groups of projected beams each one focussed on one of more scan-lines covering a certain imaging region are fired for obtaining successive image information of a certain slice of the imaging region being each group of projected beams covering the selected image region preceded by a high energy projected beam with a mechanical index suitable for completely or partially destroying contrast media present in the said imaging region and by executing the firing of each group of projected beams with different step like longer lasting time periods from the firing of the preceding group of projected beams in order to acquire so called-perfusion curves.
According to a first embodiment an automatic time basis is provided for automatically determining the moments of firing each successive projected beam or group of projected beams covering a certain area of interest. The firing of each ultrasound beam or of each group of ultrasound beams is executed in an automatic way.
According to a second embodiment which may be provided in combination with the first one as a second operative option, the firing of each group is executed manually.
As a further improvement of the above mentioned method for measurements of perfusion curves and for comparing the venous and/or arterial perfusion in the region under examination with samples of typical perfusion curves in tissues showing a specific pathology or not showing any pathology, the method provides the steps of displaying virtual images of the flow superimposed or combined with the B-mode image of the region under examination.
This may be achieved by extracting the image data for each image of the sequence of images from the known image or perfusion data of the sample tissues showing a particular pathology or not showing any pathology and by using this sample image data as the image data of the second imaging mode, i.e. the imaging mode selected for imaging the venous or arterial flow in the region under examination, in order to display this sample image data in a colored manner and combined or superimposed on the acquired B-mode images of the region under examination. A virtual sequence of images of the region is then reconstructed virtually showing the sequence of images of the region under examination as if the particular pathology would be present in that region and/or if no pathology at all would be present in that region. This virtual sequence may be displayed in a window adjacent to a further window for displaying the combined image data processed according to the B-mode and to a further processing or imaging mode particularly suitable for imaging venous or arterial flow.
In this case it is also possible to use different colors for displaying the image data processed according to the second processing or imaging mode combined with the B-mode image and the data retrieved from the stored sample images combined with the B-mode image acquired. So the user may better discriminate the probability that a pathology may exist in the region in examination.
Eventually three windows of combined image data may be displayed at the same time and adjacent to one another each window corresponding respectively to the combined image data from the two image data set obtained by the at least two imaging modes from the echo signals reflected by the region under examination, the combined image data of one image data set obtained by one of the imaging modes from the echo signals and of the image data set obtained by the sample tissues showing a particular pathology and to the combined image data of one image data set obtained by one of the imaging modes from the echo signals and of the image data set obtained by the sample tissues not showing any pathology at all. In such a way a direct visual comparison may help the user in recognizing the presence of potential pathologies.
The invention relates also to a device for ultrasound imaging according to one or more of the above mentioned method steps and showing such features as an ultrasound probe with a linear or two-dimensional array, a transmission beamformer, a receiver beamformer, at least two different processing channels for extracting/reconstructing displayable image information, means for combining the image information, and means for displaying the image information.
A method for ultrasound imaging of tissues located in a tissue image region according to one embodiment of the present invention comprises the steps of projecting at least one ultrasound beam into the tissue image region, receiving ultrasound reflections, and transducing the reflections into electric echo signals, processing the echo signals according to at least two different modes, one of the processing modes being an imaging mode and the other processing mode being a different echo processing mode for imaging particular tissues, displaying the images obtained in an interleaved or combined, such as superimposed, manner on the same screen, displaying the image obtained from the first mode with a gray-scale and displaying the image obtained by the second mode in a colored manner by choosing a color adapted to the optimum physiological capability of human eyes to discriminate the information displayed by the color level scale.
One object of the present invention is to provide an improved method for ultrasound imaging of tissues located in a tissue image region.
Related objects and advantages of the present invention will be apparent from the following description.